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Environmental Tracer Applications in Aquifers with Elevated Arsenic Concentrations in Bangladesh

Explore the prevalence of arsenic in Bangladeshi aquifers, its health impacts, and mitigation strategies. Understand the complex hydrogeological systems using environmental tracing techniques. Consider the factors influencing As mobilization for effective management.

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Environmental Tracer Applications in Aquifers with Elevated Arsenic Concentrations in Bangladesh

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  1. Environmental Tracer Applications in Aquifers with Elevated Arsenic Concentrations in Bangladesh Stute, M, Horneman, A, Schlosser, P, Zheng, Y, van Geen, A, Santella, N, Smethie, W, Ho, D, Ahmed, KM, and Hoque, MA Columbia University, Lamont-Doherty Earth Observatory, Barnard College, Queens College, Dhaka University Supported by: USEPA/NIEHS SBRP 1 P42 ES10349

  2. [As] – a global problem BGS and DPHE (2001) http://www.bgs.ac.uk/arsenic/Bangladesh/

  3. http://superfund.ciesin.columbia.edu/home.html http://superfund.ciesin.columbia.edu/niehsWeb/

  4. As drinking water standards World Health Organization (WHO) guideline: 10 mg/L US standard 10 mg/L Bangladesh standard for drinking water: 50 mg/L Range in Bangladesh: <1 to over 1000 mg/L

  5. Health effects of (chronic) As exposure • Early studies in Taiwan, Argentina, and Chile • Cardiovascular disease • Skin lesions (few years of exposure) • Cancers of the skin, lung, liver, and bladder (several decades of exposure) • Children’s intellectual function

  6. Arsenic inBangladesh 25 million people > 50µg/L (Bangladesh standard) 51 million people > 10µg/L (US/WHO standard) BAMWSP (Bangladesh Arsenic Mitigation and Water Supply Program) http://www.bamwsp.org/

  7. As in sediments (not much) Organic matter Reducing conditions (no oxygen) Why is there [As] in Bangladesh? Need: In Bangladesh: As in groundwater => 1000 ug/L As(III) As in sediment 1-10 mg/kg BGS and DPHE (2001)

  8. Bangladesh is a flat place Well As (ug/L) WHO guideline Bangladesh standard Zheng et al., 2004 BGS/DPHE (2001)

  9. …and complicated (heterogeneous) Surface, last glacial maximum Local, intermediate, and regional flow systems Ravenscroft et al., 2005

  10. Araihazar One of 464 thanas (counties) in Bangladesh Population: 300,000 Size: 170 km2 Population density: 1800 people/km2 Sources: C. Small, LDEO, Landsat 7 image from USGS EROS Data Center, Sioux Falls, SD, 1991 National Census.

  11. High spatial variability Arsenic in 5,966 wells

  12. As - depth distribution in Araihazar 6000 wells Van Geen et al., 2002

  13. Wellnests

  14. E A C B G F H Wellnests in Araihazar

  15. Stute et al, 2007 Pickens et al., 1978

  16. Hydraulic heads show large variation A B Zheng et al., 2005

  17. Conceptual model dry => wet season wet => dry season BGS and DPHE, 2001

  18. A B C E F G 2 1 0 hydraulic head relative to local river (m a.s.l.) -1 -2 -3 Banana Bridge AP2 AP6 BP3 BP6 C4 C5 E3 E5 F3 F5 G3 G5/CW -4 …but hydraulic gradients are still small river

  19. Shallow Depth Profiles

  20. 4 types of samples: Precipitation (A) Surface waters (B) Groundwater (C) Rice fields B) A) C)

  21. 1 2 8 400 3 4 6 5 river 350 6 river 7 4 8 300 9 2 10 river 250 0 Precipitation -2 200 d18O (‰) Precipitation (mm/month) -4 150 -6 100 -8 50 -10 -12 0 Sep-03 Dec-03 Mar-04 Jun-04 Sep-04 Dec-04 Mar-05 date

  22. d18O over time

  23. Time series, SW8 0 0 0 0 ) 0 0 0 0

  24. Cl- over time 150 100 50 150 0

  25. 1000 1000 Shillong Yangoon Allahabad Dhaka 100 100 Groundw. Groundw. H (TU) 3 10 10 1 1 1950 1960 1970 1980 1990 2000 year 3H3He T1/2 = 12.43y 3H/3He age t: Groundwater ‘dating’ with 3H and 3He b • 3H, 3H+3He as dye • 3H/3He as radioactive clock Use of:

  26. One field site as example Residence time 10’s of y 1000’s of y Site A, Zheng et al., 2005

  27. Degassing during recharge CE model No degassing correction for 3H/3He CE degassing and excess air correction for CFCs and SF6 4.0E-07 A B 3.5E-07 C E 3.0E-07 F G ASW+air 2.5E-07 Ne (ccSTP/g) 2.0E-07 1.5E-07 1.0E-07 5.0E-08 0.0E+00 0.E+00 2.E-08 4.E-08 6.E-08 8.E-08 1.E-07 He (ccSTP/g) Processes controlling He & Ne concentrations excess air Solubility equilibrium radiogenic He degassing

  28. shallow water temp very consistent: 26oC lower NGT due to O2 consumption? increased pressure in unsaturated zone as a result of flooding? 4 Twater 6 TNG 8 10 depth (m) 12 14 16 18 20 21 22 23 24 25 26 27 28 Temperature (C) Noble gas & water temperature

  29. Groundwater 3H+3He & 3H in precipitation Stute et al., 2007 3H+3He%time2

  30. 3H/3He age and [As] • Fairly uniform increase of As concentrations with 3H/3He age • Hydrology important factor controlling variability of As concentrations Stute et al., 2007 As%age3

  31. Two potential mechanisms: • As mobilization kinetics slow: groundwater accumulates As at a ~uniform rate • As mobilization kinetics fast: dissolved As equilibrates quickly with solid phase As, shorter groundwater residence time • higher degree of As removal • Lower dissolved As concentration

  32. Laboratory studies Release rate (unamended): 90-110 mgL-1yr-1 Radloff et al, 2007

  33. ‘dating’ with CFCs, SF6and 3H/3He Plummer et al., 2000

  34. F C A expected CFCs in groundwater • CFCs are almost completely degraded 3H/3He recharge year Horneman et al., in press

  35. CFCs in soil air • Groundwater is likely sink for CFCs in unsaturated zone Horneman et al., in press

  36. 100 CFC-11 Degradation rate CFC-11 CFC-12 Site -1 -1 yr yr 10 A ~0.4 to ~0.5 ~0.25 to ~0.3 % CFC of expected C ~5.1 to ~6 ~4.8 to ~5 1 F ~1.3 to ~1.5 ~1.6 0.1 MW-A 0 4 8 12 MW-C Time (yr) MW-F 100 CFC-12 10 % CFC of expected 1 0.1 0 4 8 12 Time (yr) CFC degradation rate in groundwater => Degradation: CFC-11 > CFC-12

  37. SF6 in soil air => SF6 excess in local atmosphere Horneman et al., in prep.

  38. SF6 in groundwater • Detectable SF6 in 3H- free groundwater Horneman et al., in prep.

  39. 3H/3He and SF6 ages Horneman et al., in prep.

  40. Potential explanations? Partitioning into organic phases? Exchange with (old) bubbles? Horneman et al., in prep.

  41. Options? Remediation options Existing wells Alternative sources New wells Surface water As removal Well switching Shallow wells Deep wells Pond water Rain collection Safi filter @$18 3-kolshi filter @$5 Tube well sand filter Maintenance Monitoring Bacterial growth Spatial variability Social resistance Dug wells Seasonality Pathogens $50 for 150 ft Installation Distribution Pond sand filter 50 families @$16 ea. Bacteria 1/100 Aquaculture Boiling Rainwater harverster 1 family @ $160/$40 ea. Storage-seasonality

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